fix resize grip rendering for new GTK+ (3.10)
rewritten the stylesheet to accommodate toolkit(?) changes

general stylesheet structure and spinner animation shamelessly stolen
from GTK+ 3 master git branch

GTK+ 3 is released under LGPLv2+, the committers listed are Alexander Larsson,
Benjamin Otte, Cosmo Cecchi, Federico Mena Quintero, Rob Bratford,
Matthias Clasen and David Trowbridge

i have suffered a great amount of frustration trying to get this
stylesheet right, but this commit message is too narrow to contain it.
suffice to say, i'm starting to consider switching to a qt environment.